1. Field of the Invention
The present invention relates to an electron gun for a cathode ray tube, and more particularly, to an electron gun for a cathode ray tube driven using a dynamic focus method.
2. Discussion of the Related Art
The resolution of a cathode ray tube (CRT) is determined by characteristics of the electron beams. The characteristics include the focal point characteristics of the electron beam. In order to obtain quality images on the display, the electron beams landing on the phosphor screen must land on all areas of the phosphor screen. For example, the electron beams must land on the center and peripheral portions of the screen and have a small halo.
In the related art CRTs the electron beam holes for red (R), green (G), and blue (B) electron beams are arranged in an in-line configuration. A magnetic field is used to deflect electron beams into a pin cushion shape for a horizontal deflection and a barrel shape for vertical deflection. As a result, the focal point of the electron beams landing in the peripheries of the screen is distorted by astigmatism, which is caused by the non-uniform magnetic fields formed in the deflection apparatus. A reduction in the CRT resolution is caused by the distortion of the focal points of the electron beams in scanning peripheries and center, that is these focal points are different.
Accordingly, a dynamic focus electron gun is employed in the related art CRTs to remedy this problem. Dynamic focusing refers to the application of a dynamic focus voltage. The dynamic focus voltage creates a higher focus voltage than the normal focus voltage when the peripheries of the screen are scanned by the electron beams. Accordingly, the focal point formation on the peripheries is compensated using this technique.
The electrons to which the dynamic focus voltage is applied are typically realized through two interconnected electrodes. The electrodes may be cup-shaped and/or plate-shaped or any combination thereof, and are generally welded together.
An electromagnetic field is formed in the area of the electron gun by a deflection magnetic field formed by the deflection apparatus. The voltage is synchronized with the horizontal deflection magnetic field signal, that is a part of the deflection magnetic field, and applied to the dynamic focus electrodes.
However, in the related art dynamic focus CRT systems, noise is generated in the area of the electron gun and interferes with the operation of the device, thereby reducing the quality of the device. Vibration of the dynamic focus electrodes generates the noise and the vibration is caused by a dynamic focus voltage applied to the electrodes. However, the dynamic focus voltage generates the electromagnetic field and electromagnetic force and causes the electrodes to vibrate.
Korean Laid-Open Patent No. 2001-0018045 discloses such a dynamic focus electron gun. Further, there is disclosed in Korean Laid-Open Patent No. 2001-0057789 an electron gun for a color Braun tube that improves an insertion depth structure of electrodes with respect to bead glass, and a structure for wires connected to electrodes and stem pins to reduce the noise.
However, in the above related art electron guns, the structure directly responsible for the generation of noise is not altered. Instead the structure in the general area is improved (i.e., the insertion sections of the electrodes that are inserted into the bead glass or the wire structure). Therefore, only a minimal reduction in noise is realized.
Noise is generated by the electrodes of the electron gun at specific frequencies, for example, at 7.4 kHz or 12 kHz. If an attempt is made to reduce noise by varying the specific frequency in the indirect and not the direct area of the noise source, that is, in the path through which the vibrations caused by the noise occur, then it becomes difficult to vary the frequency with respect to the noise source. Further, if the vibrations caused by the noise source pass through a path other than the one normally taken, then the effectiveness in reducing the vibrations through conventional methods decreases considerably.